Update concepts.mdx (#23955)

Added link to list of built-in tools.

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docs/docs/concepts.mdx

@@ -521,6 +521,8 @@ Generally, when designing tools to be used by a chat model or LLM, it is importa
 
 For specifics on how to use tools, see the [relevant how-to guides here](/docs/how_to/#tools).
 
+To use an existing pre-built tool, see [here](docs/integrations/tools/) for a list of pre-built tools. 
+
 ### Toolkits
 
 Toolkits are collections of tools that are designed to be used together for specific tasks. They have convenient loading methods.